Climate Change Characteristics And Carbon Dynamic Process Simulation Analysis Of Tropical Seasonal Rainforest

The Sakaerat（Abbreviated as SKR）research area is located in central Thailand,the forest types are mainly tropical seasonal evergreen forests.The climate is mainly affected by the southwest monsoon and northeast monsoon.The dry and wet seasons are distinct,and the interannual time scale is also affected by El Ni（?）o Southern Oscillation（ENSO）,etc.The tropical forest in the study area has the typical regional characteristics of Southeast Asia,and has strong representativeness in geographical distribution,climate and forest types.In the context of the continuous increase in global temperature,the relationship between the carbon cycle process of tropical forest ecosystems and climate change is still unclear.Especially on a regional scale,traditional research methods cannot carry out observations and calculations on long-term,large-scale forest ecosystem carbon balance processes.In view of this,this paper uses remote sensing meteorological data and MODIS satellite data to analyze the tropical seasonal evergreen forests in the SKR study area of Thailand from 1961 to 2019,the trend,mutation change characteristics and fluctuation cycles of precipitation and temperature,and reveals the characteristics of NPP multi-year changes and its response to meteorological factors.The response relationship of the factors,Base on the vorticity flux site data,the dynamic process and parameter sensitivity of forest carbon flux in the SKR study area from 2001 to 2003 were simulated and evaluated.The results are as follows:（1）The temperature increase rate in the SKR study area from 1961 to 2019 reached a rate of 0.145℃/10 a,and the multi-year average temperature was 26.83℃.The temperature change showed an extremely significant upward trend（P<0.01）,which was lower than the original temperature.The interannual temperature warming rate in the same latitude area under study（0.216℃/10 a）,and after excluding this study area through remote sensing processing,the temperature increase rate in other areas at the same latitude increased to 0.222℃/10 a.The temperature rise rate is much higher than that in the rainy season,and the temperature increase trend is significant.The Mann-Kendall test showed that the time of significant annual temperature mutation was 1990,which was consistent with the same latitude temperature change.The dry season temperature mutation time was similar to the annual average temperature.The rainy season temperature mutation took place in 1976 and 1985,respectively.The average annual temperature has periodic fluctuations of 4 a,12 a and 22 a.Among them,12 a is the first main cycle and runs through the whole year.The cyclic fluctuation trend of the dry season temperature is similar to the annual average temperature,and there are multiple periodic fluctuations in the rainy season.The first main cycle is 22 years,and there are periodic fluctuations of 3 years,5-7 a,and 25-35 years in other areas of the same latitude,and 30 a is the first main cycle.（2）In the past 60 years,the precipitation change in the study area has shown an insignificant downward trend,with a decline rate of 23.83 mm/10 a,an average of1203.83 mm in multiple years,and a rainfall decline rate of 21.58 mm/10 a in the rainy season,which is close to the dry season precipitation.The annual precipitation rate is mainly affected by the change of the rainy season precipitation rate.The Mann-Kendall test showed that the mutation time of the significant decrease in annual precipitation occurred in 1967.The dry season precipitation mutation was not obvious,and the rainy season mutation time was similar to the annual precipitation mutation test results.The annual precipitation has three periodic fluctuations of 3-6 a,10-15 a,and 20-26 a.With4 a as the first main cycle,the cyclic fluctuation of the rainy season is similar to that of the annual precipitation,and the dry season cycle has multiple fluctuation cycles.11 a is the first main cycle.（3）The change trend of vegetation net primary productivity in the study area from2001 to 2019 showed an insignificant decline.The spatial distribution was higher in the central part and lower in the surrounding area,showing a significant negative correlation with the change in average annual temperature over the same period.The annual precipitation in the same period showed a significant negative correlation.The trend of increasing volatility,but there is no significant correlation with NPP.The temperature in the dry season has a significant correlation with NPP,while the temperature and precipitation in the rainy season have no significant relationship with NPP.（4）The simulation results of the improved NCEAS monthly scale model show that the annual net primary productivity simulation results of the average precipitation of the previous six months are closest to the fitting value of the annual precipitation NPP.Precipitation correlates more strongly with NPP in the study area than does temperature.The model fitting NPP in 2002 was 562.33 g C·m^-2·a^-1,and the fitting NPP in 2003 was438.82 g C·m^-2·a^-1.（5）The carbon flux model was well fitted,and the regression analysis showed a significant linear relationship between the fitted and measured values（P<0.01）,and was able to accurately simulate the CO₂ fluxes in the Thai tropical rainforest.The CO₂diffusion process from the forest to the atmosphere has the greatest influence on the structure of carbon fluxes within the forest,and the diffusion coefficient k has extreme values at a value of 0.4;the parameters apoplastic mass M₀ and activation energy Ea are not sensitive in the model.